Radio communication repeater

ABSTRACT

The invention proposes a repeater designed for indoor transmissions. The useful frequency band is split into two frequency bands and the repeater amplifies the signals from one of the bands and translates them to the other band. The transposition of frequency bands results in preventing creating significant interference effects on the signal to be amplified. A management circuit is used to address, at lower cost, interference problems between the bands.

The invention relates to a radio communication repeater and morespecifically for indoor communication.

Radio communication repeaters are used to amplify the signal to increasethe range of a transmitter. The use of repeaters for broadcast signalsis known. A receive antenna directed at a transmitter receives thesignal which is amplified and then transmitted via another antenna theradiation of which does not cover the receive antenna. In some cases thebroadcast signal comes from a satellite and is translated to anotherfrequency band in order to be broadcast in a more restricted frequencyband.

For indoor communications, the use of frequency bands situated at around2.4 GHz and at around 5 GHz and intended for wireless domestic networksis known. However, these radio frequencies do not propagate easily, evennot at all, through walls and ceilings. Such systems struggle to coverlarge houses which have several floors and a large number of internalwalls.

One idea is to use one or more repeaters to overcome the propagationproblems associated with the indoor environment and with the frequenciesused. However, domestic networks are bidirectional networks which mustmake provision to repeat signals from various positions in multipledirections. Furthermore, these signals are strongly reflected byobstacles, creating interference with the transmitted signals.

Presently, there is no repeater designed for indoor transmissions andadapted to overcome echoes.

The invention proposes a repeater designed for indoor transmissions. Toaddress the multi-directional aspect of antennas, the useful frequencyband is split into two frequency bands and the repeater amplifies thesignals from one of the bands and translates them to the other band. Thetransposition of frequency bands helps avoid creating significantinterference effects on the signal to be amplified.

Thus, the invention is a radio communication repeater which includes afirst path to receive signals in a first frequency band, to translatethe received signals into a second frequency band and to transmit in thesecond frequency band, and a second path to receive signals in thesecond frequency band, to translate the received signals into the firstfrequency band and to transmit in the first frequency band.

According to a preferred embodiment, the repeater includes a managementcircuit to disable transmission from the first path if the second pathreceives signals first, and to disable transmission from the second pathif the first path receives signals first. The management circuitdisables the transmission means of the first and second paths when nosignal is received by the first and second paths. The disabling of thetransmission means of the first and second paths is carried out bycutting the power to amplifiers.

The invention will be better understood, and other features andadvantages will become apparent from reading the description thatfollows, with reference to the accompanying drawings in which:

FIG. 1 represents the paths of the signals translated and amplified bythe repeater according to the invention, and

FIG. 2 represents a circuit for managing the paths of FIG. 1.

In the following description, the transmission band is assumed to liebetween 5.15 and 5.825 GHz and is split into a first frequency band, forexample between 5.15 and 5.35 GHz for Europe and the USA, and a secondfrequency band, for example between 5.5 and 5.7 GHz.

FIG. 1 represents a repeater with two signal paths. The first signalpath includes a first receive antenna ARx1 connected to a first filter10 to receive and convert signals located in the first frequency band toelectrical signals, the first filter 10 being a bandpass filter with apassband corresponding to the first frequency band. A first amplifier 11amplifies the signal from the first filter 10 and delivers it to a firstmixer 12. The first mixer 12 mixes the signal from the first amplifier11 with a signal, for example of frequency 4.15 GHz, from a first localoscillator OSC1. A second filter 13 selects, from the output of thefirst mixer 12, the translated signals corresponding to an intermediateband for example between 1 and 1.2 GHz, the second filter 13 being abandpass filter with a passband corresponding to the intermediatefrequency. A second mixer 14 mixes the signals from the second filter 13with a signal, for example of frequency 4.5 GHz, from a second localoscillator OSC2. A third filter 15 selects, from the output of thesecond mixer 14, the signals corresponding to the second frequency band,the third filter 15 being a bandpass filter with a passbandcorresponding to the second frequency band. A second amplifier 16amplifies the signals from the third filter 15 and delivers them to afirst transmission antenna ATx2.

The second signal path includes a second receive antenna ARx2 connectedto a fourth filter 20 to receive and convert signals located in thesecond frequency band to electrical signals, the fourth filter 20 beinga bandpass filter with a passband corresponding to the second frequencyband. A third amplifier 21 amplifies the signal from the fourth filter20 and delivers it to a third mixer 22. The third mixer 22 mixes thesignal from the third amplifier 21 with the signal from the second localoscillator OSC2. A fifth filter 23 selects from the output of the thirdmixer 22 the signals corresponding to the intermediate band, the fifthfilter 23 being a bandpass filter with a passband corresponding to theintermediate band. A fourth mixer 24 mixes the signals from the fifthfilter 23 with the signal from the first local oscillator OSC1. A sixthfilter 25 selects from the output of the fourth mixer 24 the signalscorresponding to the first frequency band, the fifth filter 25 being abandpass filter with a passband corresponding to the first frequencyband. A fourth amplifier 26 amplifies the signals from the sixth filter25 and delivers them to a second transmission antenna ATx1.

Various embodiments of the signal paths are possible, the importantaspect being that the first frequency band is translated to the secondfrequency band while amplifying the signals, and that the secondfrequency band is translated to the first frequency band whileamplifying the signals.

Using an intermediate frequency band relaxes the constraints that wouldexist if a single translation were carried out to pass from the firstfrequency band to the second frequency band and vice versa. By using asingle intermediate band for both paths, the same oscillators can beused for both paths, thus reducing costs.

Using two amplifiers per signal path means that lower cost amplifierscan be used and the amplification process can be distributed in order toreduce the noise factor at the receive end (amplifiers 11 and 21) whilebenefiting from sufficient transmit power (amplifiers 16 and 26).Nevertheless it is possible to use a single amplifier.

Moreover, although the example describes a system using four antennas,two for reception ARx1 and ARx2 and two for transmission ATx1 and ATx2,this number of antennas can be reduced to two, one transmitting andreceiving in the first frequency band and the other transmitting andreceiving in the second frequency band. It is even possible to use asingle antenna, but this increases the filtering constraints on thefirst and fourth filters 10 and 20 for separating out the first andsecond frequency bands.

As represented in FIG. 1, there is a coupling between the antennasoperating in the same frequency bands (a coupling that is verypronounced when the same antenna is used for both transmission andreception). One solution is to use an adaptive filter on each path, forexample in place of filters 10 and 20, to suppress not only the signalamplified by the other path but also all the echoes resulting from thesignals transmitted by the other path. Such a solution is relativelycomplex to implement.

In the context of an indoor transmission system operating according tothe HiperLAN2 or IEEE 802.11a standard, a full-duplex type system is notnecessary. Thus, as a preference, it is proposed to disable one signalpath as soon as a signal is detected on the other signal path.

To this end, a management circuit retrieves the signals M1 from theoutput of the second filter 13 and the signals M2 from the output of thefifth filter 23. Based on signals M1 and M2, the management circuitgenerates control signals C1 and C2 which control the power supply tothe fourth amplifier 26 and the second amplifier 16 respectively. Assoon as a signal is detected on one of the paths, the amplifier of theother path is powered down.

To prevent unstable states, associated with the response time of themanagement circuit or the amplification of noise, the management circuitshould preferably cut off the power supply to the second and fourthamplifiers 16 and 26 when no input signal is detected.

FIG. 2 shows an example embodiment of a management circuit according tothe invention.

The management circuit includes a first and second thresholding means 30and 31 receiving respectively signals M1 and M2 and outputtingrespectively binary signals M1′ and M2′ representing the state ofsignals M1 and M2 with respect to a threshold. Each thresholding means30 or 31 is for example formed by a circuit measuring the average powerof signals Ml or M2 in the intermediate band and by a Schmitt triggerwhich outputs a logic signal M1′ or M2′ representing the average powerwith respect to a predetermined threshold. The logic signal M1′(respectively M2′) is at a logic level “0” when the signals M1(respectively M2) are below the threshold and at a logic level “1” whenthe signals M1 (respectively M2) are above the threshold.

Logic gates 32 to 35 implement an asynchronous flip-flop reflected bythe following truth table: line N° M1′ M2′ C1(t) C2(t) C1(t + δt) C2(t +δt) 1 0 0 X X 0 0 2 0 1 0 X 1 0 3 0 1 X 0 1 0 4 0 1 1 1 0 0 5 1 0 0 X 01 6 1 0 X 0 0 1 7 1 0 1 1 0 0 8 1 1 0 0 1 1 9 1 1 0 1 0 1 10 1 1 1 0 1 011 1 1 1 1 0 0

In this table, C1(t) and C2(t) correspond to the states of the controlsignals C1 and C2 respectively before a switching action of logic gates32 to 35; C1(t+δt) and C2(t+δt) correspond to the states of controlsignals C1 and C2 respectively resulting from the switching of logicgates 32 to 35. Level “0” of a control signal C1 or C2 corresponds tocutting off the power to the amplifier 26 or 16 that the signalcontrols. Level “1” of a control signal C1 or C2 corresponds to poweringup the amplifier 26 or 16 controlled by the said signal.

Line 1 corresponds to the case in which none of the paths receives.Lines 2, 3, 5 and 6 correspond to the case in which only one pathreceives signals. Lines 9 and 10 correspond to both paths receivingsignals while an amplifier was already activated, which happens when thesignal is amplified after it has been translated to the other band.

Lines 8 and 11 correspond to abnormal operation having a low probabilityof occurrence. Line 8 corresponds to unlikely cases in which both pathsstimultaneously receive signals at the input from two different sources,resulting in the simultaneous activation of the amplifiers of bothpaths. Line 11 corresponds to a state following the state of line 8,which cuts off both amplifiers. The states of lines 8 and 11 thenoscillate between each other as long as signals are receivedsimultaneously by both paths.

Lines 4 and 7 correspond to states that can occur only if the previousstate was that of line 8 and if one of the external sources stopstransmitting. The next state then corresponds to the state of one oflines 2, 3, 5 or 6.

Assuming that the probability of attaining the state of line 8 is notnegligible, it is preferable to suppress the abnormal operation. Toavoid the scenario in which the state of line 8 starts to oscillate withthe state of line 11, one of the gates 32 to 35 simply need bedimensioned such that it has a slower switching time than the othergates so as to pass either to the state of line 9 or to the state ofline 10.

Another solution is to introduce at the output of a gate a delay circuit40 the delay period 8t of which is at least equal to the switching timeof logic gates 32 to 35. If positioned as shown in FIG. 2, the delaycircuit 40 introduces an additional line in the truth table: line N° M1′M2′ C1(t) C2(t) C1(t + δt) C2(t + δt) 8′ 1 1 0 0 1 0

Since line 8′ occurs before line 8 and the delay δt is at least equal tothe switching time of gates 32 to 35, the next state corresponds to thatof line 10. Line 8 can no longer disturb the system, the statescorresponding to lines 4, 7 and 11 no longer occurring.

The management circuit of FIG. 2 is given only as a guide and can bereplaced by any other circuit that can provide management of both signalpaths as indicated previously.

Other embodiments of the invention are possible. In particular, thefirst and second frequency bands can be much more restricted in sizethan indicated previously. The frequency band allocated in Europeincludes a first band between 5.15 and 5.35 GHz and a second bandbetween 5.47 and 5.725 GHz, corresponding to a 200 MHz band and a 255MHz band that include, respectively, 9 and 11 channels of 20 MHz. Thefrequency band allocated to the USA includes a first band between 5.15and 5.35 GHz and a second band between 5.725 and 5.825 GHz,corresponding to a 200 MHz band and a 100 MHz band that include,respectively, 9 and 4 channels of 20 MHz. For a domestic installation, asingle channel is sufficient for the most part and the intermediate bandcan be reduced to a single channel. Channels are selected during theinstallation of the various devices according to the location in thepremises. The repeater must be equipped with means for selecting thechannel used as first frequency band and the channel used as secondfrequency band. The said selection means will then directly affect thefrequencies of the local oscillators OSC1 and OSC2.

1. Radio communication repeater wherein it includes: a first path toreceive signals in a first frequency band, to translate the receivedsignals into a second frequency band and to transmit in the secondfrequency band, a second path to receive signals in the second frequencyband, to translate the received signals into the first frequency bandand to transmit in the first frequency band; and a management circuit todisable transmission from the first path if the second path receivessignals first, and to disable transmission from the second path if thefirst path receives signals first. said first and second frequency bandsbeing separated.
 2. (canceled)
 3. Repeater according to claim 1, whereinthe management circuit includes thresholding means to compare thereceived signals with a receive threshold, the signals being consideredreceived if they are above the said threshold.
 4. Repeater according toclaim 1, wherein the first path includes a first translation means totranslate the signals from the first frequency band to an intermediatefrequency band and a second translation means to translate the signalsfrom the intermediate frequency band to the second frequency band, inthat the second path includes a first translation means to translate thesignals from the second frequency band to the intermediate frequencyband and a second translation means to translate the signals from theintermediate frequency band to the first frequency band, and in that therepeater includes a first local oscillator cooperating with the firsttranslation means of the first path and the second translation means ofthe second path, and a second local oscillator cooperating with thesecond translation means of the first path and the first translationmeans of the second path.
 5. Repeater according to claim 3 wherein thethresholding means compare the signals in the intermediate frequencyband.
 6. Repeater according to claim 1, wherein the management circuitdisables the transmission means of the first and second paths when nosignal is received by the first and second paths.
 7. Repeater accordingto claim 1, wherein the disabling of the transmission means of the firstand second paths is carried out by cutting the power to amplifiers.